The present invention relates to a new method for the production of alloys possessing high elastic modulus and high magnetic properties. More particularly, the invention relates to a new method for the production of ordered alloys possessing high elastic modulus and high magnetic properties by electrodeposition.
As known, electrodeposition (or electroplating) is defined as the art of production of metallic deposits through the action of electric current on a solution containing the respective metal ions to be deposited. Such coatings have the purpose of improving the appearance, corrosion resistance, hardness, bearing qualities or other properties of the basic metals, on which the coating is produced, or can be detached from the substrate and be used as tools in view of their special properties.
The technique of electroplating is widely used in many fields. There are specific cases such as springs, magnets or apparatus which require high or controlled modulus of elasticity or magnetism, when ordered alloys containing of two or more metals in alternating layers up to 100 .ANG. thickness will have to be electrodeposited on a particular substrate. The use of the common electroplating techniques, i.e., the deposition of a layer of one metal in one bath followed by the electrodeposition of a second layer of another metal in another bath, may be conceived theoretically, but practically it is not applicable due to the long duration time which the operation of electrodeposition will involve and the complexity involved. Usual deposition of two metals from a common bath results in the production of alloys that are not ordered or structured in discrete layers of the practically pure components of the objects to be coated, or the layers are not thin enough to acquire the necessary elastic or magnetic properties.
A few years ago, a proposal was made for obtaining composition modulated alloys which possess the required properties of elasticity and magnetism, using the technique of vapor deposition (T. Tsakalakos et. al., J. Physique C-7, 404, 1977). According to this method, composition modulated layers of copper-nickel were prepared by co-evaporating the two components through a rotating pinwheel shutter onto a mica substrate at a temperature of 350 degrees centigrade. But the method has various disadvantages, e.g. high cost of production, and limitations in size and shape of the objects to be coated.
The essential parts of a typical electroplating system are:
(1) the plating bath which contains a compound of the metal to be deposited; PA1 (2) a source of direct current electricity; PA1 (3) the substrate to be coated; and PA1 (4) a counter electrode. PA1 P.sub.M =the concentration of the noblest metal in the layer of less noble metal expressed, in % grain equivalents; PA1 I.sub.L =the limiting current density for the noblest metal electrodeposition depending on metal concentration and agitation; PA1 I.sub.T =the total current density applied during the electrodeposition of the less noble metal layer; and PA1 .eta.=cathodic efficiency. PA1 (a) wavelength of the modulation; PA1 (b) average composition of the alloy; and PA1 (c) modulation's amplitude.
The negative terminal of the direct current source, is connected to the substrate (the cathode) while the positive terminal is connected to the counter electrode (the anode). When both of these electrodes are immersed in the plating bath, oxidation occurs at the anode and metal ions migrate to the cathode surface and are transformed to the metallic state and attached to that surface. The thickness of a plated coating is determined by the time of electroplating and the current density employed.
The pulse plating technique is a recognized method in the electroplating industry. The method consists in the turning on and off continuously in rapid succession the current applied to the electroplating bath. During the pulse "on" time, the ions are electroplated out of solution at the cathode interface. During the pulse "off" time, the solution near the cathode interface becomes replenished with metal ions.
The technique of electrodeposition of two or more individual metals from one single solution, each metal to be deposited in a substantially pure form in such a way as to obtain enhanced modulus of elasticity and magnetism was unknown prior to the present invention. The reason why such attempts could not succeed, was explained by a thermodynamical assumption based on the fact that the noblest metal will deposit simultaneously with the less noble metal, or that the deposition of alternate layers at the required thickness was impossible by electrodeposition.
In a very recent paper by D. Tench and J. White (Metallurgical Transactions A. Vol. 15A, November 1984, p. 2039-40) composites of Ni-Cu layers are described which were electrodeposited from a bath, mentioning their enhanced tensile strength. The composites consisted actually of a rigid material (i.e. Ni) embedded in a soft matrix (i.e. Cu) like many known composites, and had neither enhanced modulus of elasticity nor any improved magnetic properties. Therefore, these composites could never be utilized for special applications requiring these properties.